First aid dressing for wounds or burns

ABSTRACT

A first aid dressing for wounds or burns to prevent gross infection of the burns or wounds from air or water-borne bacteria, dust, dirt, etc. which comprises a microporous breathable thermoplastic film of sufficient size to cover the burn or wound and preferably an uninjured perimeter around the burn or wound and means around the perimeter of the microporous film, such means being able to provide a closure of the microporous film dressing to the perimeter around the burn or wound, the closure being sufficiently secure to prevent gross entry of air between the dressing and the skin. In use, when so applied, the first aid dressing, which is usually non-adherent to the wound or burn, is inflated away from the wound or burn by means of positive pressure created by moisture vapor issuing from the burn or wound or the uninjured parts of the body which are covered by the first aid dressing or entrapped air heated by the skin. The first aid dressing is permeable to air and moisture vapor, but impermeable to liquid water and other liquids which do not wet the hydrophobic film and also to air-or water-borne bacteria, etc.

United States Patent 11 1 Snyder 1 11 3,324,998 [451 July 23, 1974 FIRSTAID DRESSING FOR WOUNDS OR BURNS [75] Inventor: George W. Snyder,Hudson, NJ.

[73] Assignee: Celanese Corporation, New York,

[22] Filed: Oct. 12, 1971 [21] Appl. No: 188,317

[52] US. Cl. 128/157, 128/132 R [51] Int. Cl. A611 13/00 [58] Field ofSearch 128/157, 132, 83, 165, 128/184, 260, 400, 82, 154, 156, 159

[56] References Cited UNITED STATES PATENTS 1,980,486 11/1934 King etal128/132 R 3,324,580 6/1967 Baxter 128/165 UX 3,329,143 7/1967 Gordon128/82 3,610,238 10/1971 Rich 128/184 FOREIGN PATENTS OR APPLICATIONS648,733 1/1951 Great Britain 128/156 1,163,130 4/1958 France 128/132 R641,061 8/1950 Great Britain 128/132 R 7/1962 France 128/132 R PrimaryExaminerLawrence W. Trapp Attorney, Agent, or FirmThomas J. Morgan;Linn 1. 9999M??? 13m [5 7] ABSTRACT A first aid dressing for wounds orburns to prevent gross infection of the bums or wounds from air orwater-home bacteria, dust, dirt, etc. which comprises a microporousbreathable thermoplastic film of sufficient size to cover the burn orwound and preferably an uninjured perimeter around the burn or wound andmeans around the perimeter of the microporous film, such means beingable to provide a closure of the microporous film dressing to theperimeter around the burn or wound, the closure being sufficientlysecure to prevent gross entry of air between the dressing and the skin.In use, when so applied, the first aid dressing, which is usuallynon-adherent to the wound or burn, is inflated away from the wound orburn by means of positive pressure created by moisture vapor issuingfrom the burn or wound or the uninjured parts of the body which arecovered by the first aid dressing or entrapped air heated by the skin.The first aid dressing is permeable to air and moisture vapor, butimpermeable to liquid water and other liquids which do not wet thehydrophobic film and also to air-or water-borne bacteria, etc.

1.129119%. Prair naFisu PATENIED 3.824.998

INVENTOR.

660/96 W Snyder WZM ATTORNEY FIRST AID DRESSING FOR WOUNDS OR BURNS Thisinvention relates to a first aid dressing for the prevention of grosscontamination and infection by airor water-borne bacteria of burns orwounds.

When in the course of human events, tragedy in the form of severe woundsor burns befalls either an individual or groups of people engaged indangerous pursuits such as war, many times the wounds or burns sustainedare not the major cause of concern but rather secondary contamination ofthe wound or more serious infection of the wound or burn caused byair-borne bacteria or Water-borne bacteria, etc. For example, if

, someone is severely burned in an automobile accident where a gasolinetank explodes, there is a major chance of infection occurring from thetime of the burn to the time when the patient is admitted to a hospitaland treatment is begun. Similarly, where in jungle combat, a soldier orgroups of soldiers are wounded by mortar rounds which tear gaping woundsin the torso exposing the viscera, secondary infection or contaminationof the wound often times provides greater cause for concern than thewounds themselves.

Ordinary bandages of sterile gauze and the like are of limited use incombatting contamination and gross infection because they are grosslypermeable to all manner of air-borne and also water-borne contaminationand sources of infection. Similarly, ordinary nonporous plastic filmsare of little or no utility because,

while they might tend to keep out air-borne and water-' bornecontamination and sources of infection, they also deprive the wounded orburned area of oxygen; and if left on for sufficiently long periods oftime, instead of inhibiting sources of infection, they would tend topromote an anaerobic infection. Non-porous films render the covered areahot and sweaty. The first aid dressings of the present invention combatthe foregoing and other disadvantages of the prior art.

The present invention comprises a microporous polymeric film as moreparticularly described hereinafter together with a means of fasteningtheperimeter of the microporous film to preferably an uninjured perimeterof the body which surrounds the wounded or burned area which is desiredto be protected from gross contamination and sources of infection.

The appended figures illustrate but a few of the different embodimentsof the present-invention.

FIG. 1 illustrates a human arm which has a wound (w). The arm includingthe wounded portion is enclosed in an elongated tubular microporous filmstruc ture sealed across one end (10). The arm, of course, is insertedinto the structure at the open end. That end is substantially tightlyattached to the arm above the wound area by means such as adhesive tape,a draw string (11, illustrated) or a fiat elastic band attached to theopen end of the bag.

FIG. 2 shows a bag, which may be considered a sort of duffel bagarrangement, again an elongated tubular structure sealed across one end(10). The patient who is wounded (w) or burned in the lower extremitiesand possibly the lower portion of the torso is inserted into the bag andmeans (11) such as described above for FIG. 1 are used to substantiallytightly close the open end of the bag to the patient around themidsection, for example, which is above the wounded area. A longer bagmight be utilized which would enclose the patient up to a higher portionof the anatomy; for example, it might be closed about the necksufficiently tight for purposes of this invention and yet not so tightthat it would restrict breathing or swallowing of the patient.

FIG. 3 illustrates a human torso with a wounded (w) or burned area inthe abdomen. In this case, it may be preferable to employ the first aiddressing of this invention in the form of a rather large film which hasabout its perimeter a continuous or substantially continuous band ofadhesive. The film (12) is positioned so that the central non-adhesivearea is over the wound or burn. Adhesive perimeter (13) is continuousand seals the film securely around the wound, preferably to theuninjured area sorrounding it.

FIG. 4 shows a structure basically similar to that illustrated in FIG.1; however, it differs in that it has a simple valve comprised of (14)and (l5). (14) is a tubular member attached to and open to structure(10); and (15) is a pinch clamp, shown clamping off (14).

FIGS. 5 and 6 are two views of a small dressing (20). FIG. 5 is a viewof the part that is toward the skin when in use. FIG. 6 is a crosssectional view, the dressing being sectioned 'as shown in FIG. 5. InFIGS. 5 and 6,

(21) is the microporous breathable thermoplastic film;

(22) is a ring of suitable material (preferably same polymer as film) ofappropriate thickness to space the film away from a burn or wound, onesurface of the ring being attached to the film; and (23) is a coating ofadhesive on the opposite surface of the ring.

In whatever form, the first aid dressing depicted in FIGS. 1 to 4 shouldbe sufficiently large that they can balloon away from the injured areaunder the action of the positive pressure caused by moisture vaporissuing from the covered area. In the dressing depicted in FIGS. 5 and6, the ring serves to space this relatively small dressing away.

As pointed out above, the first aid dressing of this invention has acombination of unique properties not found in any other heretofore knowndressing which enable it to be used in the first aid of wounds or burns,etc. to prevent the entry into such wounds or burns of air-borne orwater-borne contamination or sources of infection. The first aiddressings do not adhere to the wounded or burned area. They areessentially inert and in addition are readily sterilized by known means.They permit the relatively free passage of air from outside the dressingthrough the microporous wall of the dressing and into contact with thewounded area or burned area. They permit the relatively free egress fromthe wounded area or burned area of moisture vapor issuing from theuninjured skin area or from the wounded or burned area itself. This isimportant since it renders the dressing relatively comfortable, whichwould not be the case where a non-porous polymeric film had been used.That would keep the skin clammy and moist. In such a case, the build-upof sweat or body fluids on the wounded or burned area might not be inthe best interest of prevention of contamination or infection. This, aspointed out, is alleviated or prevented through use of the first aiddressings of this invention. The film is permeable to moisture vaporissuing from the skin, but permeable to such an extent that thereresults in the space between the dressing and the wound a positivepressure caused by the moisture vapor, which causes the dressing toballoon away from the wound to a greater or lesser degree depending onthe area covered and the size of the dressing.

Porous or cellular films can be classified into two general types: onetype in which the pores are not interconnected, i.e., a closed-cellfilm, and the other type in which the pores are essentiallyinterconnected through tortuous paths which may extend from one exteriorsurface orsurface region to another, i.e., open-celled film. Themicroporous films useful in the present invention are of the lattertype.

The microporous films useful in the present invention are alsocharacterized by a reduced bulk density, sometimes hereinafter referredto simply as a low density. That is, these microporous films have a bulkor overall density lower than the bulk density of corresponding filmscomposed of identical polymeric material, but having no open-celled orother voidy structure. The term bulk density as used herein means theweight per unit of gross or geometric volume of the film, where grossvolume is determined by immersing a known weight of the film in a vesselpartly filled with mercury at 25C. and atmospheric pressure. Thevolumetric rise in the level of mercury is a direct measure of the grossvolume. This method is known as the mercury volumenometer method, and isdescribed in the Encyclopedia of Chemical Technology, Vol. 4, page 892(Interscience 1949). v

Porous films have been produced which possess a microporous, open-celledstructure, and which are also characterized by a reduced bulk density.Films possessing this microporous structure are described, for example,in U.S. Pat. No. 3,426,754. The preferred method of preparationdescribed therein involves drawing or stretching at ambienttemperatures, i.e., cold'drawing, a crystalline, elastic starting filmin an amount of about to 300 percent of its original length, withsubsequent stabilization by heat setting of the drawn film under atension such that the film is not free to shrink or can shrink only to alimited extent.

While the above described microporous or voidcontaining film of theprior art is useful in certain applications, the search has continuedfor new processes able to produce open-celled microporous films having agreater number of pores, a more uniform pore concentration ordistribution, a larger total pore area, and better thermal stability ofthe porous film. These properties are significant in applications suchas filter media where a large number of uniformly distributed pores arenecessary or highly desirable; and in applications such as breathablemedical dressings subject to high temperatures, e.g., sterilizationtermperatures, where thermal stability is necessary or highly desirable.

An improved process for preparing open-celled microporous polymer filmsfrom non-porous, crystalline, elastic polymer starting films includes 1)cold stretching, i.e. cold stretching the elastic film until poroussurface regions or areas which are elongated normal or perpendicular tothe stretch direction are formed, (2) hot stretching the cold stretchedfilm until fibrils and pores or open cells which are elongated parallelto the stretch direction are formed, and thereafter (3) heating or heatsetting the resulting porous film under tension, i.e., at substantiallyconstant length, to impart stability to the film. Yet another process issimilar to this process but consolidates steps (2) and (3) into acontinuous, simultaneous, hot stretching-heat setting step, said stepbeing carried out for a time sufficient to render the resultingmicroporous film substantially shrink resistant (less than about 15percent).

The elastic starting film or precursor film useful in this invention ispreferably prepared from crystalline polymers such as polypropylene bymelt extruding the polymer into a film, taking up the extrudate at adrawdown ratio giving an oriented film, and thereafter heating orannealing the oriented film, if necessary, to improve or enhance theinitial crystallinity.

The essence of the improved microporous process is the discovery thatthe sequential cold stretching and hot stretching steps impart to theelastic film a unique open-celled structure which results inadvantageous properties, including porosity and improved thermalstability. A further enhancement of porosity occurs when the film istreated with certain organic liquids such as perchloroethylene.

As determined by various morphological techniques or tests such aselectron microscopy, the microporous films are characterized by aplurality of elongated, nonporous, interconnecting surface regions orareas which have their axes of elongation substantially parallel.Substantially alternating with and defined by these nonporous surfaceregions which are a plurality of elongated, porous surface regions whichcontain a plurality of parallel fibrils or fibrous threads. Thesefibrils are connected at each of their ends to the non-porous regions,and are substantially perpendicular to them. Between the fibrils are thepores or open cells of the films utilized by the present invention.These surface pores or open cells are substantially interconnectedthrough tortuous paths or passageways which extend from one surfaceregion to another surface area or region.

With such a defined or organized morphological structure, the filmswhich are treated according to the improved process may have a greaterproportion of surface area that the pores cover, a greater number ofpores, and a more uniform distribution of pores, than previousmicroporous films. Further, the fibrils present in the films of theimproved invention are more drawn or oriented with respect to the restof the polymer material in the film, and thus contribute to the'higherthermal stability of the film. I

The total surface area per cubic centimeter of the films used in thisinvention is in the range of from 2 to about 200 square meters per cc.Preferably the range is from about 5 to about 100 square meters per cc.and most preferably from about 10 to about square meters per cc. Thesevalues can be compared with normal pin-holed film which has a totalsurface area per gram of about 0.1 square meters; paper and fabric whichhave values per gram of about 1.0 square meters and leather which has avalue of about 1.6 square meters per cc. Additionally, the volume ofspace per volume of the films used in this invention ranges from about0.05 to about 1.5 cubic centimeters per gram, preferably from about 0.1to about 1.0 cubic centimeters per gram and most preferably from 0.2 toabout 0.85 cubic centimeters per gram. Additional data to define thefilms used in this invention relates to nitrogen flux measurements,wherein the microporous films have Q (or nitrogen) Flux values in therange of from about 5 to 400 perferably about 50 to 300. These valuesgive an indication of porosity, with higher nitrogen flux valuesindicating higher levels of porosity.

Nitrogen flux may be calculated by mounting a film having a standardsurface area of 6.5 square centimeters in a standard membrane cellhaving a standard volume of 63 cubic centimeters. The cell ispressurized to a standard differential pressure (the pressure dropacross the film) of 200 pounds per square inch with nitrogen. The supplyof nitrogen is then closed off and the time required for the pressure todrop to a final differential pressure of 150 pounds per square inch asthe nitrogen premeates through the film is measured with a stop watch.The nitrogen flux, Q, in gram moles per square centimeter minute, inthen determined from the equation:

Q (27.74 X /At X T) where At is the change in time measured in secondsand T is the temperature of nitrogen in degrees Kelvin. The aboveequation is derived from the gas law, PV ZnRT, wherein P is pressure; Vis volume; Z is the compressibility factor; n is the number of moles ofgas; R is the gas constant per mole; and T is the absolute temperature.

Precursor films useful in the processes for making microporous films areelastic films of crystalline, filmforming polymers. These elastic filmshave an elastic recovery at zero recovery time (hereinafter defined)when subjected to a standard strain (extension) of 50 percent at 25C.and 65 percent relative humidity of at least about 40 percent preferablyat least about 50 percent, and most preferably at least about 80percent.

Elastic recovery as used herein is a measure of the ability of astructure or shaped article such as a film to return to its originalsize after being stretched, and may be calculated as follows: 7 A

Elastic Recovery (ER) length added when stretched strain is merelyexemplary. In general, such starting films will have higher elasticrecoveries at strains less than 50 percent, and somewhat lowerrecoveries at strains substantially higher than 50 percent, as comparedto their elastic recovery at a 50 percent strain.

Thesestarting elastic films will also have a percent crystallinity of atleast percent, preferably at least 30 percent and most preferably atleast 50 percent, e.g., about 50 to 90 percent, or more. Percentcrystallinity is determined by the x-ray method described by R. G. Quynnet al. in the Journal of Applied Polymer Science, Vol. 2, No. 5, pp.166-173 1959). For a detailed discussion of crystallinity and itssignificance in polymers, see Polymers and Resins, Golding (D. VonNostrand, 1959).

Preferred suitable starting elastic films, as well as the preparationthereof, are further defined in British Pat. No. 1,198,695, publishedJuly 15, 1970. Other elastic films which may be suitable for thepractice of the present invention are described in British Pat. No.1,052,550, published Dec. 21, 1966, and are well known in the art.

The starting elastic films utilized in the preparation of the permeablefilms used in the present invention should be differentiated from filmsformed from classical elastomers such as the natural and syntheticrubbers. With such classical elastomers the stress-strain behavior, andparticularly the stress-temperature relationship, is governed by anentropy-mechanism of deformation (rubber elasticity). The positivetemperature coefficient of the retractive force, i.e., decreasing stresswith decreasing temperature and complete loss of elas- Although astandard strain of 50 percent is used to identify theelastic propertiesof the starting films, such tic properties at the glass transitiontemperature, are consequences of entropy-elasticity. The elasticity ofthe starting elastic films utilized in preparing microporous films,however, is of a different nature. In qualitative thermodynamicexperiments with these elastic starting films, increasing stress withdecreasing temperature (negative termperature coefficient) may beinterpreted to mean that the elasticity of these materials is notgoverned by entropy effects but dependent upon an energy term. Moresignificantly, the starting elastic films have been found to retaintheir stretch properties at temperatures where normal entropy-elasticitycould no longer be operative. Thus, the stretch mechanism of thestarting elastic films is thought to be based on energy-elasticityrelationships, and these elastic films may then be referred to asnon-classical elastomers.

As stated, the starting elastic films employed in preparing themicroporous films used in this invention are made from a polymer of atype capable of developing a significant degree of crystallinity, ascontrasted with more conventional or classical elastic materials such asthe natural and synthetic rubbers which are substantially amorphous inther unstretched or tensionless state.

A significant group of polymers, i.e., synthetic resinous materials,which may be used are the olefin polymers, e.g., polyethylene,polypropylene, poly-3-methyl butene-l, poly-4-methyl pentene-l, as wellas copolymers of propylene, S-methyl butene-l, 4-methyl pentene-l, orethylene with each other or with minor amounts of other olefins, e.g.,copolymers of propylene and ethylene, copolymers of a major amount of 3-methyl butene-l and a minor amount of a straight chain n-alkene such asn-octene-l, hexadecene-l, noctadene-l or other relatively long chainalkenes, as well as copolymers of 3-methyl petene-l and any of the samen-alkenes mentioned previously in connection with 3-methyl butene-l.These polymers in the form of film should generally have a precentcrystallinity of at least 20 percent, preferably at least 30 percent,and most preferably about 50 percent to percent or higher.

For example, a film-forming homopolymer of polypropylene may beemployed. When propylene homopolymers are used, it is preferred toemploy an isotactic polypropylene having a percent crystallinity asindicated above, a weight average molecular weight ranging from about100,000 to 750,000, preferably about 200,000 to 500,000 and a melt index(ASTM- 8D-l238-57T, Part 9, page 38) from about 0.1 to about 75,preferably about 0.5 to 30, so as to give a final film product havingthe requisite physical properties.

While the present disclosure and examples are directed primarily to useof the aforesaid olefin polymers, the invention also contemplates thehigh molecular weight acetal, e. g., oxymethylene polymers. While bothacetal homopolymers and copolymers are contemplated, the preferredacetal polymer is a random oxymethylene copolymer, one which containsrecurring oxymethylene, i.e., --CH --O-, units interspersed wtih -ORgroups in the main polymer chain where R is a divalent radicalcontaining at least two carbon atoms directly linked to each other andpositioned in the chain between the two valences, with any substituentson said R radical being inert, that is, those which do not includeinterfering functional groups and which will not induce undesirablereactions, and wherein a major amount of the OR units exist as singleunits attached to oxymethylene groups on each side. Examples ofpreferred polymers include copolymers of trioxane and cyclic etherscontaining at least two adjacent carbon atoms such as the copolymersdisclosed in US. Pat. No. 3,027,352 of Walling et a1. These polymers infilm form should also have a crystallinity of at least 20 percent,preferably at least 30 percent, and most preferably at least 50 percent,e.g., 50 to 60 percent or higher. Further, these polymers have a meltingpoint of at least 150C., and a number average molecular weight of atleast 10,000. For a more de- .tailed discussion of acetal andoxymethylene polymers,

see Formaldehyde, Walker, pp. 175191 (Reinhold Many of the microporousfilms useful to make the first aid dressings of this invention arereadily disposable after use by incineration. Acetal polymers aresuperior in this regard.

Other relatively crystalline polymers to which the invention may beapplied are the polyalkylene sulfides such as polymethylene sulfide andpolyethylene sulfide, the polyarylene oxides such as polyphenyleneoxide, the polyamides such as polyhexamethylene adipamide (nylon 66) andpolycaprolactam (nylon 6), and polyesters such as polyethyleneterephthalate, all of which are well known in the art and are notdescribed further herein for the sake of brevity.

The types of apparatus suitable for forming the starting elastic filmsto be used to make microporous films for the first aid dressings of thisinvention are well known in the art.

For example, a conventional film extruder equipped with a shallowchannel metering screw and coat hanger die, is satisfactory. Generally,the resin is introduced into a hopper of the extruder which contains ascrew and a jacket fitted with heating elements. The resin is melted andtransferred by the screw to the die from which it is extruded throughaslot in the form of a film from which it is drawn by a take-up orcasting roll. More than one take-up roll in various combinations orstages may be used. The die opening or slot width may be in the range,for example, of about 10 to 200 mils.

Using this type of apparatus, film may be extruded at a drawdown ratioof about 20:1 to 200:1, preferably 50:1 to 150:1.

The terms drawndown ratio or, more simply, draw ratio, as used herein isthe ratio of the film wind-up or take-up speed to the speed of the filmissuing at the extrusion die.

The melt temperature for film extrusion is in general no higher thanabout 100C. above the melting point of the polymer and no lower thanabout 10C. above the melting point of the polymer.

For example, polypropylene may be extruded at a melt temperature ofabout 180C. to 270C preferably 1 200C. to 240C. Polyethylene may beextruded at a melt temperature of about 175C. to 225C., while acetalpolymers, e.g., those of the type disclosed in US. Pat. No. 3,027,352may be extruded at a melt temperature of about 185C. to 235C, preferably195C. to 215C.

The extrusion operation is preferably carried out with rapid cooling andrapid drawdown in order to obtain maximum elasticity. This may beaccomplished by having the take-up roll relatively close to theextrusion slot, e.g., within two inches and, preferably, within oneinch. An air knife operating at temperatures between, for example, 0C.and 40C., may be employed within one inch of the slot to quench, i.e.,quickly cool and solidify the film. The take-up roll may be rotated, forexample, at a speed of 10 to ft/min., preferably 50 to 500 ft/min.

While the above description has been directed to slot die extrusionmethods, an alternative method of forming the starting elastic films forthe microporous films used in this invention is the blown film extrusionmethod wherein a hopper and an extruder are employed which aresubstantially the same as in the slot extruder described above. From theextruder, the melt enters a die from which it is extruded through anannulus to form a tubular film having an initial diameter D Air entersthe system through an inlet into the interior of said tubular film andhas the effect of blowing up the diameter of the tubular film to adiameter D Means such as air rings may alsobe provided for directing airabout the exterior of the extruded tubular film so as to provide quickand effective cooling. Means such as a cooling mandrel may be used tocool the interior of the tubular film. After a short distance duringwhich the film is allowed to completely cool and harden, it is wound upon a take-up roll.

Using the blown film method, the drawdown ratio is preferably 20:1 to200:1, the slot opening 10 to 200 mils, the D /D ratio, for example, isfrom 0.5 to 6.0 and preferably about 1.0 to about 2.5, and the take-upspeed, for example is 30 to 700 ft/min. The melt temperature may bewithin the ranges given previously for slot extrusion.

The extruded film may then be initially heat treated or annealed inorder to improve crystal structure, e.g., by increasing the size of thecrystallites and removing imperfections therein.

In order to render the precursor, or starting, film microporous, it issubjected to a process generally comprising the steps of stretchinguntil micropores are formed and heat setting to stabilize the thusformed pores of the starting film. Preferably the process compriseseither the consecutive steps of cold stretching, hot stretching and heatsetting or the steps of cold stretching and simultaneously hotstretching and heat setting the precursor film. Other variations on thisprocess (such as elimination of the hot stretching step) can be carriedout, resulting in microporous films which, although slightly inferior tothose films made by the cold stretch hot stretch a heat set process,still find utility in the microporous first aid dressings of thisinvention.

The term cold stretching as used herein is defined as stretching ordrawing a film to greater than its original length and at a stretchingtemperature, i.e., the temperature of the film being stretched, lessthan the temperature at which the melting of the film begins when thefilm is uniformly heated from a temperature of 25C. at a rate of 20C.per minute. The term hot stretching" or hot stretching-heat setting asused herein is defined as stretching above the temperature at whichmelting begins when the film is heated from a temperature of 25C. at arate of 20C. per minute, but below the normal melting point of thepolymer, i.e., below the temperature at which fusion occurs. Forexample, using polypropylene elastic film, cold stretching is carriedout, preferably, below about 120C. while hot stretching or hotstretching-heat setting is carried out utive stretching steps occur isin the range of about to about 300 percent of the original length of thefilm prior to stretching.

The resulting microporous film exhibits a final cyrstallinity ofpreferably at least 30 percent, more preferably about 50 to 100 percentas determined by the aforementioned x-ray method and as previouslydefined an elastic recovery from a 50 percent extension of at least 50percent, preferably 60 to 85 percent. Furthermore, this film exhibits anaverage pore size of about 100 to 12,000 Angstroms more usually 150 to5,000 Angstroms, the values being determined by mercury porosimetry asdescribed in an article by R. G. Quynn et al., on pages 21-34 of TextileResearch Journal, Jan. 1963.

Additional description, of the different methods for the preparation ofmicroporous films is contained in copending U.S. application, Ser. No.835,367 filed on June 23, 1969,-copending U.S. application, Ser. No.876,511 filed on Nov. 13, 1969, copending U.S. application Ser. No.84,712 filed on Oct. 28, 1970, and copending U.S. application, Ser. No.104,715 filed on Jan. 7, 1971.

The means for fastening the first aid dressing of this invention to thevictims are of such nature that a seal is formed between the victim andthe dressings that will permit the positive pressure generated bymoisture vapor issuing from the covered area of the patient to at leastpartially inflate the dressing away from the injured area which iscovered by the dressing. Any suitable means may be used. Examples ofsuch means are drawstrings about the open perimeters of, for example,dressings of the sort illustrated in FIGS. 1 and 2, elastic bandsaffixed to those perimeters which have a series of gripper snaps toallow for correct adjustment, or tapes affixed to those perimeters whichhave a Velcro closure device so positioned as to allow correctadjustment to the victim.

The first aid dressings which are flat, rather than tubular with aclosed end, may be affixed over the wounded or burned area by means ofan adhesivecoated perimeter, preferably on the microporous dressingitself. The adhesive is preferably a continuous but microporous pressuresensitive adhesive coating. This adhesive is preferably a rubbery-basedadhesive which is water-insoluble and viscoelastic, and the coating isaggressively tacky in its normal dry state. This adhesive coating isfirmly anchored to provide a unitary integrated structure that will notbe delaminated or split when the tape is unwound.

The present invention contemplates the use of any highly gas andmoisture permeable adhesive coating for the film herein. Preferably, theprocess of forming the continuous adhesive'coating around the perimeterof the film is of such a nature that, during the drying of the coating,innumerable, pore-like apertures spontaneously develope therein andthese pores result in a viscoelastic porous adhesive membrane coveringthe porous backing. These pores are so minute that they are not visibleto the human eye upon casual inspection of the film-the adhesive coatingthus being of a visibly continuous nature. They are, however, ofsufficient size and closeness together to permit of ample transpirationof skin moisture and wound vapors. and to permit of absorption of liquidmaterial therethrough into the porous film backing. The effect isessentially uniform over the entire contacted body area; asdistinguished from the effects produced by tapes which have relativelylarge holes or apertures therein, or which have been perforated byneedles, or which have discontinuous spacedapart strips or spots ofordinary impermeable adhesive on a porous backing, to obtain a so-calledbreathable" tape, as suggested in the prior art. The continuous uniformmicroporous recticular nature of the continuous adhesive perimeteraround the film is a decided advantage.

If desired, use can be made of rubber-base pressuresensitive adhesivecoating compositions that are free from extraneous or undesirablenon-volatile components or ingredients, and from liquid plasticizers,thereby avoiding the presence in the dried adhesive coating ofsubstances which impair adhesion or cohesion or which may cause orpromote skin irritation. For instance, use can be made of pureviscoelastic polymers which are inherently aggressively tacky and highlycohesive and which are relatively non-irritating to the human skin, suchas the pressure-sensitive acrylate polymers. This latter adhesive is notonly waterinsoluble but it is hydrophobic as indicated by the fact thatdrops of water deposited on the surface do not flow out and wet thesurface. The microporosity of the adhesive coating obviates the need ofincluding any moisture-absorptive material in the adhesive composition.1

In a preferred embodiment for the fabrication of the dressings of thisinvention, the viscoelastic pressuresensitive adhesive is applied to theporous backing film in such a way as to provide thereon a continuoussoft sticky viscid coating containing a volatile vehicle which is insmall enough proportion to avoid wicking or penetration of the adhesivethrough the body of the porous film backing when it is-promptly driedafter application. Further drying of the semi-dry adhesive coatingresults in progressive loss of the residual volatile vehicle and ashrinkage of the coating. These capillary and shrinkage effects producea strain in each tiny portion of the viscoelastic adhesive film whichbridges a backing passageway and in yielding to this strain one or moreminute openings (pores) are autogenously formed therein. In this way theentire adhesive coating, during drying autogenously develops a vastnumber of closely spaced pores per square inch producing a microporousreticulated structure in an adhesive film that remains visiblycontinuous and provides a unitary microporous film-adhesive web.

The necessary degree of adherency of the dressing is not prevented bythe presence of these pores. The viscoelastic property of the adhesiveprevents the pores from closing up even during prolonged pressing of theadhesive in storage.

Use of an adhesive which is agressively tacky but is more rubbery andfirmer than conventional surgical tape adhesive (which are loaded withsofteners and pigments) is desirable, and is provided by the previouslya 1 I mentioned acrylate polymer adhesive. Such a dressing can beremoved more readily and comfortably from the skin after prolongedcontact and yet is readily applied and immediately adhere. to the skinwith adequate adhesion when pressed into place. Furthermore, theelasticity of the film backing utilized herein can be maintained, e.g.,at 50 percent extension a recovery of 80 percent can be obtained, sothat the tape or dressing will retain and hold the skin in its initialposition.

Application of the adhesive to the porous film backing may beaccomplished by a variety of methods. One convenient way to carry outthis process is first to prepare in the usual way a solution of theadhesive in sufficient solvent (volatile vehicle) to provide a coatableviscosity. This adhesive solution is then coated in the desiredperimeter shape and size on a liner web having a dense nonporous,shiny-smooth surface of an antistick nature that will permit of readyseparation from the adhesive coating in its subsequent semi-dried andfully dried states. This adhesive coating is partially dried bypassingthe web into a hot air drying oven or over a heated drum, and isbrought into laminar bonding contact with a superimposed web of theporous backing. The resulting sandwich web is then promptly furtherheated to eliminate the residual solvent from the adhesive coating,during which interval the adhesive coating acquires the desired porousstate (which is retained in the fully dried product) and upon completionof the drying operation to fully remove the solvent, it is wound up in ajumbo roll. Drying of the applied adhesive coating perimeter layer isconducted with sufficient 'promptness to prevent the adhesive fromsoaking or striking through the body of the porous film backing. Theevaporating solvent is free to escape through the porous backing web.Drying of the adhesive coating while at all stages in contact with theimpermeable, smooth, shiny surface of the liner, results in the driedadhesive coating having a smooth dense outer surface characteristic.During the porosity-inducing phase of the drying, the adhesive contactto the liner is disrupted at the points where the pores are formed. Thisis permitted by the anti-stick surface which allows the adhesive to pullaway from it where the pores develop, leaving the surrounding adhesivesurfaces in continued contact with the liner surface.

This dried composite sheeting is subsequently unwound from the jumboroll and the adhesive-coated films and liner are slit between perimetersof adjoining dressings. For use the liner is stripped from the dressingand discarded. While in place during storage, however, it keeps thedressing side that will subsequently be toward the wound free fromcontamination.

Instead of using a liner web in the manufacture of the tape (as justdescribed), the adhesive solution can be combined with a smooth-surfacedanti-stick liner web and handled as previously described. It will beevident that these procedures also result in a tape having a smoothadhesive surface.

Other methods of forming an adhesive perimeter may 7 also be used.

The transpiration porosity of the tape is such as to provide a moisturevapor transmission rate that exceeds the perspiration emission rate ofthe human skin under ordinary conditions. The permeable or porousadhesive coating is hydrophobic but is (in common with other suchadhesives) capable of softening and swelling upon prolonged contact withliquid perspiration. However, due to transpiration of perspirationthrough the pores, there is much less tendency for the adhesive tosoften or lose tackiness upon prolonged contact with perspiring skinthan is the case where the ordinary non-porous type of adhesive is used.Perspiration from the underlying skin can pass through the adhesivecoating either as vapor, or as liquid which is absorbed by the porouscapillary structure of the backing and thence evaporated, so that in anycase the skin is maintained in a dry state under ordinary conditions.These features result in retention of the tape and the skin in theinitial position.

The flat film dressing which is selfinflating as hereinbefore describedshould have sufficient free area to allow sufficient room to inflate thedressing. Usually the free area which will become inflated should be atleast about 10 square inches.

For flat film first aid dressings of smaller area, it is preferred thata walled adhesive-coated perimeter be utilized, which will space thedressing away from the wound. Such a dressing is shown in FIGS. 5 & 6.The walled perimeter may be of any sufficiently flexible ma terial whichwill contour itself to the area of the body to be covered. Thosepolymers mentioned above for preparation of the microporous dressing, aswell as others, may be used for the walled perimeters, which need not bemicroporous. It will usually be practical to employ the same class ofpolymers for theperimeter walls as was used to make the microporousdressing. The walls should be of sufficient height to space themicroporous dressing away from the wound. Generally, heights ofone-sixteenth inch to about three-sixteenths inch are useful. The widthsof the walls are generally not critical. They should be wide enough,however, to

permit the application of sufficient adhesive, which will maintain thedressing securely covering the wound.

In any of the dressings of this invention but particularly the largertubular ones illustrated in FIGS. 1 and 2, there may be incorporated inthe dressing a valve with means for opening and closing access to theenclosed dressing by gases, liquids, or solids so that they can beintroduced into or extracted from the atmosphere in the closed dressing.Such a dressing is shown in FIG. 4. Gases liquids, or solids, which canbe introduced can either promote healing, or be bacteriostatic orbactericidal, or anesthetic, or perform combinations of these and otherfunctions. Oxygen is known to promote healing and may be introduced inproper mixtures for that purpose. Gaseous or vaporous bactericides,bateriostats and anesthetics are well known.

EXAMPLE I A first aid dressing of the sort mentioned in connection withFIG. 1 and made of microporous polypropylene (produced in accordancewith the foregoing description) was pulled up over a human arm and thetop of the dressing secured about the upper arm area to form asubstantially air-tight seal. After several minutes the first aiddressing, which was initially limp about the arm, became inflatedthrough the action of the positive pressure of the moisture vaporissuing from the arm. The first aid dressing was essentially not incontact with the arm but rather freely floated at some distance from it.At no time was the arm clammy or sweaty from the encasement in the firstaid dressing, rather, it felt cool and comfortable in the dressing.

EXAMPLE II A inches X 10 inches X 1 mil microporous polypropylene firstaid dressing with a one-half inch wide adhesive perimeter, which isproduced in accordance with the foregoing description, is placed over ahuman abdomen. Within minutes the adhesive-free central portion of thedressing is inflated away from the abdomen by the action of the positivepressure of moisture vapor issuing from the covered skin. The coveredarea is dry,'and not at all clammy or sweaty, as would be the case witha nonporous plastic film.

EXAMPLE in A walled-perimeter microporous dressing is prepared frommicroporous polypropylene film 2 inches in diameter and 1 mil thick byheat sealing the edge to the top of a one-eighth inch thick 0 shapedring of polypropylene with the width of the 0 one-fourth inch. Anadhesive coating was coated on the bottom of the 0. The adhesive side ofthe finished dressing is then placed against a human cheek, where aftera short while the microporous dressing becomes slightly domed from theaction of the partial pressure of moisture vapor issuing from the skin.

EXAMPLE IV Example I is repeated but with an optional modification ofthe dressing. The modification comprises the heat sealing of acommercial plastic valve to the dressing. Again the dressing is affixedto an arm, but this time oxygen from a cylinder is introduced throughthe valve into the atmosphere in the dressing thereby enriching theenclosed air in the dressing. The valve is then closed. Depending onporosity, size of the dressing, etc., the higher concentration of oxygenin the air in the enclosed dressing will slowly equilibrate with thelower concentration of oxygen in the atmosphere outside the dressing bya process of diffusion through the microporous dressing.

Some microporous films may have good tensile strength in one direction(machine) and poor tensile strength in the other direction (transverse).If this proves to be a problem in a particular dressing, the film may bereinforced by cross laminating with another layer of the film with theabove directions at to each other. Other means of reinforcing may alsobe used.

What is claimed is:

1. A first aid dressing comprising an inflatable micorporous polymericfilm, said film having an average pore size in the range of betweenabout to 12,000 Angstroms, having a shape adapted to cover and enclose awound or burn and means about the perimeter of the first aid dressing bywhich the dressing can be securely affixed around the wound or burn.

2. The first aid dressing of claim 1 in which the microporous film is amicroporous polypropylene film.

3. A first aid dressing as claimed in claim 2 in which the microporouspolypropylene film dressing has an average pore size in the range ofbetween about and 5,000 Angstroms.

4. The first aid dressing of claim 1 which is in the form of a tubularstructure sealed across one end.

5. A first aid dressing as claimed in cliam 4 in which the open end ofthe tubular structure has a draw string attached thereto.

6. A first aid dressing as claimed in claim 4 wherein the open end ofthe tubular structure has affixed around its perimeter an elasticclosure.

7. A first aid dressing as claimed in claim 6 wherein the elasticclosure is a flat elastic band.

8. The first aid dressing of claim 4 in which there is incorporated inthe dressing a valve as a means for opening and closing access to theenclosed dressing by gases, liquids, or solids.

9. A first aid dressing as claimed in claim 1 in which the dressing isin the form of a flat film with means about its perimeter to securelyaffix the dressing about the wound or burn.

10. A first aid dressing as claimed in claim 9 in which on one side ofthe film and substantially continuously extending about its perimeterthere is an adhesive band.

11. A first aid dressing as claimed in claim 9 which is affixed to thetop of a wall around its perimeter and the means for affixing thedressing around the wound or burn is an adhesive coating on the bottomof the wall.

2. The first aid dressing of claim 1 in which the microporous film is amicroporous polypropylene film.
 3. A first aid dressing as claimed inclaim 2 in which the microporous polypropylene film dressing has anaverage pore size in the range of between about 150 and 5,000 Angstroms.4. The first aid dressing of claim 1 which is in the form of a tubularstructure sealed across one enD.
 5. A first aid dressing as claimed incliam 4 in which the open end of the tubular structure has a draw stringattached thereto.
 6. A first aid dressing as claimed in claim 4 whereinthe open end of the tubular structure has affixed around its perimeteran elastic closure.
 7. A first aid dressing as claimed in claim 6wherein the elastic closure is a flat elastic band.
 8. The first aiddressing of claim 4 in which there is incorporated in the dressing avalve as a means for opening and closing access to the enclosed dressingby gases, liquids, or solids.
 9. A first aid dressing as claimed inclaim 1 in which the dressing is in the form of a flat film with meansabout its perimeter to securely affix the dressing about the wound orburn.
 10. A first aid dressing as claimed in claim 9 in which on oneside of the film and substantially continuously extending about itsperimeter there is an adhesive band.
 11. A first aid dressing as claimedin claim 9 which is affixed to the top of a wall around its perimeterand the means for affixing the dressing around the wound or burn is anadhesive coating on the bottom of the wall.